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Posted by Part#Man on Friday, February 29, 2008 at 21:16:34 :
In Reply to: Re: There is no vacuum at WOT. posted by John Dunn on Friday, February 29, 2008 at 16:42:11 :
Depends on the vacuum advance used. The spring-loaded airtight diaphragm vacuum advance uses only vacuum, no weights. The breaker plate is supported by a bearing. The vacuum line goes to the atmospheric side of the carb's throttle valve. At idle there is no vacuum. As soon as the throttle is opened, air passing the vacuum passage draws air from the vacuum line causing the diapragm to move aginst the spring advancing the plate and timing.
Bottom line - the vacuum advance can add an addition 15 degrees advance or more beyond the capability of centrifugal weights at the same MPH. The FFPW uses an engine designed for agricultural use at slow speeds on low octane. There was not the need envisioned in its use, for a vacuum advance.